Gearboxes are integrated into a large number of mechanical systems, to transmit a movement between two parts rotating at different speeds, i.e., to establish a speed ratio different from 1 between the two parts. In particular, such gearboxes frequently connect a motor to an axle driven by the motor, for example in railway vehicle cars.
Gearboxes frequently comprise an input shaft, an output shaft and an intermediate shaft transmitting a movement from the input shaft to the output shaft, these shafts cooperating with one another via gears arranged to establish the speed ratio different from 1. In order to provide as efficient a transmission of energy as possible, the gears of the gearbox are generally lubricated with a liquid such as an oil.
However, many geometric constraints weigh on the gearboxes. For example, the bulk of the other elements of the mechanical system in which the gearbox is integrated frequently requires that the input and output shafts be perpendicular to one another, or that the input and output shafts be arranged at different heights.
Known from document FR 2,106,978 A5 is a device for transmitting a force between a motor and an axle, this device comprising shafts arranged at different heights relative to the ground. However, the shafts are distributed in two separate casings so as to allow relative movement of the motor and the axle, and the shafts received in a same casing are arranged at different heights from one another. This device therefore has large dimensions, in particular in the vertical direction.
Also known is a gearbox in which the input shaft is located at a height greater than that of the output shaft, the output shaft being perpendicular to the input shaft. The intermediate shaft is perpendicular to the output shaft and connected thereto by a conical gear. Conical gears are particularly susceptible to the appearance of friction, and therefore require more effective lubrication than other types of gears, such as spur gearings.
In order to provide effective lubrication of the conical gear, the gearing element carried by the output shaft bathes in an oil reserve located in the lower part of a casing housing the shafts and the gears of the gearbox. Thus, when the gearbox is operating, the gearing element of the output shaft drives the oil to the conical gear, which is thus lubricated.
The oil reserve being located in the lower part of the casing, the oil sprayed on the walls of the casing is recovered by gravity, which makes it possible to ensure that the oil reserve is not completely emptied during operation.
However, gearboxes of this type are only appropriate, due to their geometry and bulk, for certain applications. In particular, they have a significant width in a horizontal plane at the output shaft, and therefore the axle of a railway vehicle bogie in which they are integrated.